Amyotrophic lateral sclerosis (ALS) causes degeneration of motor neurons. Motor neuron loss within lumbar regions of the spinal cord leads to limb paralysis while loss of cervical respiratory motor neurons remains a defining moment in disease progression, leading to ventilatory failure and ventilator dependence. While investigations of pathogenic cellular mechanisms that underlie ALS are yielding important and novel insights, this approach has not yet produced new drugs that significantly improve the health of ALS patients. Since the cellular mechanisms of motor neuron death may be extremely complex and difficult to block with a single small molecule, we propose a more pragmatic approach. The broad long term objectives and aims are to protect or restore motor neurons by either (i) harnessing intrinsic mechanisms of plasticity, (ii) providing trophic support or (iii) repacement using human embryonic stem (hES) cells. To achieve these aims, three highly interactive projects will assess motor neuron function and survival in a well established rat model of ALS. Project 1 will use anatomical, physiological and behavioral approaches to determine the precise changes in respiration that occur in the ALS rat, and whether the death of motor neurons within this system can be modulated through stimulation of endogenous plasticity. Project 2 will explore whether a combination of stem cell derived glial cells and trophic factors such as GDNF, IGF-1, VEGF and BDNF can reduce motor neuron cell death and enhance function in the ALS rat. Project 3 will use cutting edge methods of deriving motor neurons from hES cells and establish whether they can survive in the ALS rat spinal cord and make new contacts with muscle. Questions regarding the respective roles of growth factors, astrocytes and motor neurons in the pathology of motor neuron degeneration will be constantly addressed throughout this project. The Pi's are established researchers in their fields of respiratory neurobiology, human fetal stem cells, growth factors and hES cells. They will work synergistically, share results and ideas and move towards the common goals of this P01 grant. This study directly addresses the major goal of the NIH: i.e. essential knowledge will be gained about a specific incurable disease that will have an impact on the health of patients. Furthermore, many of the approaches taken have direct relevance to treatment strategies as transplantation of stem cells is a real future possibility for this devastating disorder.